1. Field of the Invention
This invention relates to a weft gripper drive for looms, the weft which is being pulled through the shed by at least one grab that is fixed to an end of a flexible belt, that is driven to and fro by an oscillating wheel.
2. Prior Art
The known weft gripper drives with flexible lance or tape can be subdivided into two large groups, depending on whether the lance is driven by a toothless driving wheel or by a gearwheel. This invention makes part of the second group.
Both groups have in common, among other things, the problem to realize an efficient contact between tape and wheel--with a minimum wear and heating--in order to realize a sufficiently precise movement of the gripper.
In the first group, steel tapes are being used that are driven by heavy toothles drive wheels. In order to keep and conduct the solid steel tape around and in constant contact with the rather intricate wheel, all sorts of complicated devices have been tried, such as hold-down rollers and anti-friction rollers (GB No. 342.253; 424.966; U.S. Pat. No. 2,604,123; FR No. 2.217.541), magnets (U.S. Pat. No. 2,810,403), arched shoe-blocks (U.S. Pat. No. 2,888,956), pneumatic systems (U.S. Pat. No. 1,277,766) etc. Such devices require the use of lubricants and coolants in order to reduce wear and heating, with all the drawbacks involved.
In the second group, plastic perforated tapes and gear-wheels are being used, that emmesh into each other. Concerning the guiding of the tape around part of the circumference of a gear-wheel, different systems are being proposed:
anti-friction rollers (CH No. 585.293); PA0 cylindrical self-lubricating segments, for example made of graphite (U.S. Pat. No. 3,490,498); PA0 guiding of a double lance along .+-.180.degree. of the circumference of the wheel by means of the guiding device in both zones where the tape leaves the wheel (DE No. 2.02.765); PA0 special wheel that enmeshes with the tape along 50.degree.-180.degree. (GB Nos. 1.510.791, 1.510.792). PA0 two pairs of hold-down rollers that enmesh with the tape at both sides of the perforations (NL No. 77.14.245); PA0 horizontal wheel and three hold-down rollers (GB No. 1.396.492); PA0 long curved brake-like shoes (EP No. 65.231).
It became apparent that none of the known devices could operate in a really satisfactory manner, especially at the high weaving speeds required at present.
Heating and wear problems are always present, so that tapes have to be replaced relatively soon, which will prejudice productivity.